Heretofore, there has been known to transmission means which can carry compression load as well as tension load besides torque to be transmitted.
Further, it is known that rotational torque can be transmitted only with much difficulties, when an input shaft extends in parallel to an output shaft with an appreciable off-center therebetween. To ensure torque transmission in such a case as mentioned above, an Oldham coupling is usually employed.
The conventional Oldham coupling is constructed such that it contains an intermediate disc of which front and rear faces are formed with U-shaped grooves respectively oriented at a right angle to one another, said U-shaped grooves being adapted to come in sliding engagement with projections on both the driving and driven shafts. Thus, the result is that it is applicable only to a case where they have a very small center distance therebetween.
Further, it has been found with the conventional Oldham coupling that sliding friction increases in proportion to an increase in number of rotations of the input shaft. To obviate the above-mentioned drawback it was proposed that an Oldham coupling contains a reciprocating plain bearing disposed between an intermediate block and both the input and output shafts (c.f. Japanese Laid-Open Utility Model NO. 161,445/79).
The proposed Oldham coupling is constructed merely with a number of needle rollers as bearing means which are arranged on the retainers. Thus, the bearing means tend to fall down when the coupling is mounted in an orientation other than the vertical direction. Even when it is mounted in the vertical direction, there is a danger that the bearing means are disconnected from the intermediate block due to the centrifugal force caused by an increased number of rotations.